1. Field of the Invention
This invention generally relates to electrochemical cells and, more particularly, to a flow-through air cathode battery using a zinc slurry extruding anode.
2. Description of the Related Art
Flow-through batteries have been intensively studied and developed for large-scale energy storage due to their long cycle life, flexible design, and high reliability. A battery is an electrochemical device in which ions (e.g. metal-ions, hydroxyl-ions, protons, etc.) commute between the anode and cathode to realize energy storage and conversion. In a conventional battery, all the components including anode materials, cathode materials, separator, electrolyte, and current collectors are packed into a volume-fixed container. Its energy and capacity of are unchangeable as long as the battery is assembled. A flow-through battery consists of current collectors (electrodes) separated by an ion exchange membrane, while its anode and cathode materials are stored in separate storage tanks. The anode and cathode materials are circulated through the flow-through battery in which electrochemical reactions take place to deliver and to store energy. Therefore, the battery capacity and energy are determined by (1) electrode materials (anolyte and catholyte), (2) the concentrations of anolyte and catholyte, and (3) the volumes of anolyte and catholyte storage tanks.
An air battery may be considered to be a flow-through cathode battery where oxygen in the air is continuously passed over a reactive metal electrode to act as a cathode. An electrolyte typically separates the cathode from a metal or a metal compound anode. Zinc is a favored material, and it may be in a solid phase or in a particle form to enable a flow-through anode. Conventional batteries using a flow-through zinc particle anode suffer from the large amounts of electrolyte required to avoid passivation around zinc particles. Further, the zinc particle anode requires continuous pumping, and the viscosity needed to support pumping results in a low zinc concentration.
One example of a mechanically rechargeable metal-air battery using a slurry anode that addresses the above-mentioned problems is provided in parent application Ser. No. 14/473,713. On the one hand, the slurry needs to have minimal electronic resistivity so a high loading of conducting solids, i.e. active metal and carbon, is necessary. However, the high loading of solids increases slurry viscosity, so the efficient filling and removal of slurry requires the battery to have either (a) a large gap between anode-cathode current collectors, or (b) a small active area. Using an exemplary version of this mechanically rechargeable zinc-air battery, an active area of 16 square centimeters (cm2) and gap of 3-5 millimeters (mm) is obtained. However, a relatively high pressure is required to fill the slurry cavity. Also, the battery RInt (primarily slurry resistance) limits power to 100 milliamperes per square cm (mA/cm2). To scale up the power output, the battery active area would need to increase by an order of magnitude, and a novel way of delivering slurry would be needed.
It would be advantageous if a flow-through zinc anode battery existed with a large active area, with an effective way of replenishing spent slurry with active slurry.